Our research centers on the ecology, evolution,
systematics, and -omics of symbiotic fungi, and on the diversity and
roles of their secondary metabolites. As a group, we are inspired by
the astonishing diversity of the organisms we study. Here’s a tour of a
few of our recently supported research topics.

Boreal forests represent earth's largest
terrestrial biome and some of our planet's most threatened and
important drivers of global carbon- and hydrologic cycles. Through a
five-year NSF award, we are working with collaborators at Duke
University, NC State University, and the University of Minnesota to
characterizing the diversity of culturable and unculturable fungi
associated with iconic species of boreal lichens and plants at seven
sites around the circumboreal belt. Fungi obtained in our surveys will
be used for genomic and transcriptomic analyses of function, coupled
with infection trials and assessments of secondary metabolite
production. Data obtained from our work will be used to enhance current
methods to delimit and identify fungal species from environmental
samples. Coupled with rich population-level studies, deep
phylogenetics, and bioinformatics development, our field- and lab
studies will provide an unprecedented perspective on the ecological
roles, taxonomic diversity, and functional traits of important and
diverse endophytes in critically imperiled forests on three continents.

Fungal pathogens are increasingly
recognized as an important source of adult-plant and seedling mortality
in tropical forests, influencing tree demography, distributions, and
diversity. However, very little is known regarding the cryptic effects
of tropical seed-infecting fungi, including endophytes, pathogens, and
saprotrophs that decay seed tissues in soil. Seed-infecting fungi are
likely to be especially important for tree species depending upon seed
survival in soil (seed banks) for successful recruitment, including
pioneer species - the trees that rapidly exploit treefall gaps and
comprise the first steps in tropical forest succession. We are working
with Drs. Jim Dalling (University of Illinois) and Adam Davis (USDA) to
characterize seed fate in soil through a large-scale common garden
experiment at Barro Colorado Island, Panana. Our work synthesizes
field studies of seed demography with molecular analysis of fungal
communities, providing a first glimpse at the diversity, spatial
structure, and ecological roles of these little-known fungal
assemblages.

Fungal endophytes live within healthy
plant tissues without causing disease. These fungi represent apparently
avirulent symbionts that are closely related to pathogenic species, and
recent analyses have shown that endophytism and pathogenicity are
intimately linked over the evolution of the Ascomycota. These
observations raise the question: what factors influence the virulence
of fungi associated with living plant tissues? Several other labs have
shown that endosymbiotic bacteria inhabiting fungi can influence the
virulence of their hosts. Work by Michele Hoffman in our lab showed
that apparently pure genomic DNA from fungal endophyte cultures often
contains bacterial DNA. We are testing the hypothesis that bacterial
endosymbionts influence the fungal phenotype and ultimately, the
outcome of plant-fungus interactions. Under leadship by Dr. Dave
Baltrus (UA) we're part of a team to examine the genomic architecture
and phenotypic effects of these intriguing symbionts.

Endophytes are increasingly recognized
as a trove of biochemical richness, often yielding novel compounds and
pharmaceutically or industrially important metabolites. We are working
with collaborators on four projects that focus on natural product
chemistry, with team members based at the University of Arizona,
Mississippi State, Zagaya/Berkeley, the Smithsonian Tropical Research
Institute, and the Universidad de Panama, with the goal of identifying
bioactive fungin in deserts, diverse temperate and boreal
environments, and tropical forests. Our targets include breast cancer,
prostate cancer, antibiotic-resistant bacteria, and the causal agents
of malaria, leishmaniasis, and Chagas' disease. Through this work we
are evaluating ecological distributions of endophytes and other fungi
associated with plant parts such as cactus spines and tree thorns,
often through citizen-scientist workshops and outreach to high school
students.

Funding:
National
Institutes of Health (R01 and P41); US Army; consultantship on
ICBG award in Panama (NSF/NIH/USDA); Western National Parks
Association

Photo: Mariana del Olmo Ruiz

• Beta diversity of tropical fungal
endophytes

Fungal endophytes are highly abundant and
diverse in leaves of tropical trees, but the scale of their diversity
is unclear: disparate studies are generally not comparable due to
differences in endophyte isolation methods and fungal species concepts.
Accordingly, beta diversity of tropical endophytes remains unknown, and
the degree to which different ecological or geographic factors shape
endophyte communities has not been examined. With the development of
the network of Forest Dynamics plots through the Center for Tropical Forest Science, we
have a critical tool for coherent studies of alpha diversity at
multiple sites; for explicit examination of beta diversity among sites;
and for hypothesis testing with regard to the importance of forest
diversity, host plant frequency, and abiotic factors such as
precipitation in shaping host-endophyte associations. We are conducting
a three-year study to assess the endophytic flora of three tropical
forests (Mudumalai Forest Reserve, India; Korup, Cameroon; Barro
Colorado Island, Panama). Our study asks: what factors shape fungal
symbiont communities in tropical forests?

Fungal endophytes are ubiquitous among
terrestrial plants, can confer significant ecological benefits on their
hosts, are closely related to pathogens, and move across borders during
plant introductions. However, little is known regarding their diversity
and species composition in most host plants, and their cryptic roles in
facilitating invasion by the plants that harbor them have not been
explored. We are conducting an 18-month study to examine the ecological
roles of fungal endophytes in the context of one of the most dramatic
landscapes in the arid west: the Colorado Plateau, with a special focus
on Diné Bikéyah (the Navajo Nation). The goals of this
project are (1) to provide a first understanding of the morphological
and molecular diversity of fungal communities associated with native
and non-native plants of Diné Bikéyah; (2) to examine
diverse symbiont communities for taxa with potential use in biological
control of tamarisk (salt-cedar), one of the most devastating invaders
in western waterways; and (3) to provide a unique, on-Nation research
experience for Navajo undergraduates through Diné College, Tsaile,
Arizona.